1. Field of the Invention
The present invention relates an exposure device for use in a printer, a facsimile, a copying machine, etc.
2. Description of the Related Art
There has been known an image forming device such as a printer in which a latent image is formed on a surface of a photosensitive body and then developed with a developer, an image developed by the developer is transferred to a sheet, and a transferred image is fixed onto the sheet by a fixing unit.
FIG. 23 shows the structure of a conventional optical write head. As shown in the figure, the conventional optical write head includes a shift register 11 to which parallel data DATA00-15 of 16 bits, a shift clock CLK and a start signal DSTAR are inputted, a register 12 to which the output of the shift register 11 and a latch signal LST are inputted, and a large number of LEDs (Light-Emitting Diodes) 13 aligned so as to conduct exposure for one line. The optical write head also includes switching elements 14 for controlling the on/off of the LEDs 13 and AND circuits 15 for controlling a logical product of the output of the register 12 and a drive signal DST to the switching elements 14 as a control signal.
In exposing for one line, the start signal DSTR is first inputted to the optical write head. And then, in synchronism with the shift clock CLK, image data as the parallel data DATA00 to 15 for one line is inputted to the optical write head 16 bits by 16 bits. Thereafter, on the completion of the supply of the image data for one line, the latch signal LST and the drive signal DST are inputted to the optical write head.
On inputting the start signal DSTR, the shift register 11 starts to take the parallel data DATA00-15, and shifts data stored in the shift register 11 while taking new parallel data DATA00-15 every time the shift clock CLK is inputted to the shift register 11. On inputting the latch signal LST, the register 12 latches data for one line which is outputted from the shift register 11 to output the data. The AND circuits 15 to which the output of the shift register 11 is inputted, supplies a signal identical in level with a signal outputted from the shift register 11 to the switching element 14, when the drive signal DST is inputted to the AND circuits 15. Accordingly, only the LED 13 corresponding to the bit to which the shift register 11 outputs a high signal emits a light. Then, this state is maintained for a predetermined time so that exposure for one line is conducted in correspondence to the inputted image data. Thereafter the supply of image data relating to a succeeding line is conducted in the same procedure in order to make exposure for the succeeding line.
However, in the case of manufacturing an optical write head with the structure, shown in FIG. 23, including the large number of LEDs structures one line, a time proportional to the number of LEDs is required for setting data for one line.
For that reason, in order to reduce a time required for setting data for one line, there has been proposed an optical write head in which the optical write head (the shift register and the LEDs) is divided into plural groups and in which data is transferred in a parallel manner to the shift register belonging to each of those groups. For example, Japanese Patent Unexamined Publication Sho 58-48562 discloses an optical write head in which LEDs are divided into a plurality of groups, and plural circuits for driving the LEDs are provided in each group. As to thus structured optical writing head, an excellent printing result cannot be obtained because a light emission timing disperses although data setting is made at a high speed.